Frons Oyster (or Flat Tree Oyster)
Phylum: Mollusca, Class: Bivalvia, Order: Ostreida, Family: Ostreidae, Genus: Dendostrea, Species: Dendostrea frons · Ostreidae (True Oysters) · Bivalve (two-shelled). The specimen shown is a single valve (either the upper/right valve or an attached lower valve). Shape is irregularly oval to sub-circular with distinctive foliated margins.
Species
Dendostrea frons (Confidence: 85%)
Shell Type
Bivalve (two-shelled). The specimen shown is a single valve (either the upper/right valve or an attached lower valve). Shape is irregularly oval to sub-circular with distinctive foliated margins.
Family
Ostreidae (True Oysters)
Size
Estimated 1.5 to 2.5 inches (40-65mm). This is a mid-sized adult. The species typically ranges from 1 to 3 inches.
Color & Pattern
Base color is a creamy, nacreous white with a prominent, dark chocolate-brown to deep purple-brown marginal band and radial streaks. The interior is pearly white with a distinct brown muscle scar. The pattern is irregularly radial, following the plications (folds) of the shell edge.
Rarity
Common to Very Common. These are frequently found along shorelines near mangrove forests or rocky outcrops in the Cabo region.
Habitat
Found in shallow marine intertidal to subtidal zones. They commonly attach to the roots of mangroves, sea whips (gorgonians), or coral rocks in warm tropical waters.
Geographic Range
Western Atlantic and East Pacific; common around Mexico (including Cabo San Lucas and the Sea of Cortez), Florida, the Caribbean, and down to Brazil.
Description
A striking bivalve characterized by its roughly circular to oval shape and highly irregular, wavy (plicate) margins. The exterior is layered and scaly (foliaceous), while the interior possesses a smooth, pearly luster. The most defining aesthetic is the dark brown pigmentation near the crenulated edges, which creates a 'sunburst' or 'ringed' effect against the white center.
Key Features
Sharp, zig-zag marginal folds; a single, large, central muscle scar; and the ability to grow 'clasping' extensions (commissures) when attached to cylindrical objects like gorgonian stems.
Collector Value
Minimal to Moderate ($2 - $10). While not rare, clean specimens with vibrant brown-and-white contrast are popular for educational displays and decorative beach-themed collections.
Condition Notes
Good. The shell shows natural growth patterns and minimal beach wear. The periostracum is mostly worn away, revealing the calcified layers beneath. The margins are relatively sharp, suggesting it wasn't tumbled in high surf for long. Condition Grade: Fine.
Interesting Facts
Unlike edible rock oysters, Dendostrea frons is famous for its 'fingers'—small hook-like growths on the bottom valve that allow it to securely wrap around the thin branches of sea whips, effectively living off the seafloor.
Ecological Role
Filter feeder that helps clear the water of suspended particles. They provide habitat for small crabs and worms that hide within their ruffled edges. Currently not a species of conservation concern.
Similar Species
Isognomon alatus (Flat Tree Oyster) which is flatter and more rectangular; Lopha cristagalli (Cockscomb Oyster) which has much larger, deeper V-shaped zig-zags.
Beach Finding Tips
Look near mangrove roots or among wash-up debris after a storm. In Cabo, search rocky tide pools or areas where sea fans wash ashore, as these oysters are often still attached to the coral skeletons.
Notes
Cabo